Previous battery chargers have been expensive to construct, bulky, and relatively heavy in view of their use of line frequency transformers and filters such as transformers, inductors, and capacitors designed for 60 cycle operation. Such transformers typically have a substantial amount of core material and operate at a relatively low efficiency compared to power transformers which operate at a substantially higher frequency.
It is a disadvantage of previous battery chargers that they cannot automatically switch back and forth between a so-called "float mode" explained hereafter and a so-called "equalize mode", also explained hereafter.
For various types of applications, such battery chargers must properly charge a discharged battery, particularly one that has been fully discharged, in order to avoid dangerous outgassing and to avoid shortening the life expectancy of such batteries, which can be very expensive.
Furthermore, in prior art battery charging systems, the systems typically cannot provide various types of battery charge in optimum fashion, and frequently require manual intervention in switching between various types of charging modes such as normal charge and trickle charge. For example, for a heavily discharged battery, sulfation will have normally occurred and it is necessary to not only charge the battery but also equalize the cells, i.e. bring all cells to the same voltage and to desulfate these cells. Furthermore, if a battery is overcharged, particularly during equalization and desulfating, excessive gases can be emitted which are highly undesirable. Furthermore, damage to the battery can result through overcharging. Also, once a battery has been fully charged and equalized, the battery can gradually discharge while it sits on the shelf, particularly depending upon the temperature and internal resistance of the battery. The higher the temperature, the shorter the shelf life and the greater the internal discharge of the battery which will occur with time. Another disadvantage of prior art battery chargers is the inability to compensate for wide variations in line voltage, such as may occur during field operation on power systems which are not well regulated or controlled. Furthermore, particularly in industrial applications, it is important to minimize "ripple" in the output dc. Such ripple can be line frequency ripple or load induced ripple. This is particularly true when the battery charger acts as the primary power source and the battery is employed like a "filter" to handle current surges. Previous chargers have thus required expensive components to reduce ripple to a value which will not harm the battery during charging.
A further disadvantage is that prior art battery chargers have been unable to provide various types of charging functions automatically and without manual intervention. Although some prior art battery chargers have attempted to simulate automatic equalization charging through use of preset timers, such chargers have the disadvantage that they do not respond to the actual dynamic condition of the battery at a given moment in time to determine whether or not further equalization charging is appropriate.